Configuring a Null Route

You can configure a null static route to drop packets to a certain destination. This is useful when the traffic should not be forwarded if the preferred route is unavailable.
Note: You cannot add a null or interface-based static route to a network if there is already a static route of any type with the same metric you specify for the null or interface-based route.

The following figure depicts how a null static route works with a standard route to the same destination.

Null Route and Standard Route to Same Destination

The following procedure creates a preferred route and a null route to the same destination. The null route drops packets when the preferred route is not available.

  1. Enter global configuration mode. 
    device# configure terminal
  2. Configure the preferred route to a destination. 
    device(config)# ipv6 route 2001:DB8::0/64 ve 3 fe80::1
    This example creates a static route to IPv6 2001 : DB8 : : 0/64 destination addresses. These destinations are routed through link-local address fe80::1 and the next hop gateway virtual interface (ve) 3. The route uses the default cost metric of 1.
  3. Configure the null route to the same destination with a higher metric. 
    device(config)# ipv6 route 2001:DB8::0/64 null0 2
    This example creates a null static route to the same destination. The metric is set higher so that the preferred route is used if it is available.

The following example creates a primary route to all 2001 : DB8 : : 0/64 destinations through virtual interface (ve) 3. It creates an alternative null route to drop the packets when the primary route is not available. 

device# configure terminal
device(config)# ipv6 route 2001 : DB8 : : 0/64 ve 3 fe80::1
device(config)# ipv6 route 2001 : DB8 : : 0/64 null0 2
Parent topic: IPv6 Static Routing